Page 3 - Lesson Note-4-Ch-13 SA and Volume(Sphere)

5.Total Surface Area (TSA)of hollow hemi − sphere = Area of base + CSA
2
2
2
2
= [ ( − ) +2 ( + ) ] sq.unit


2
2
=  R −  r + 2 R + 2 r 2

2

3 R +  = 2  r 2
2
3
6.Volume of Hollow hemi sphere = ( − ) cubic unit
3
3

Example-1
Find the surface area of a sphere of radius 4.2 cm.
Solution
r = 4.2 cm.

Surface area of the sphere

= 221.76 cm .
2

Example-2

Find (i) the curved surface area and (ii) total surface area of a hemi sphere of radius
21 cm.
Solution: Radius = 21 cm
(i) CSA = 2 = 2 × 22 × 21 × 21 = 2772
2
2
7
2
(ii) TSA= 3 = 3 × 22 × 21 × 21 = 4158
2
7
Example-3

A hemi spherical dome of a building needs to be painted. If the circumference of the
base of the dome is 17.6 m, find the cost of painting it, given the cost of painting is
Rs. 5 per 100
2

Solution:

Circumference of base = 17.6 m

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